Update `TopologyGraph.from_openff_topology` for new API

[mattwthompson]

PR Summary:

The Topology class in the OpenFF toolkit is undergoing a heavy refactor, including removing some API points that Foyer uses. The refactor will not be in a release for some months, but we are actively testing downstream packages by installing against a feature branch. The parts of the refactor that are relevant here are unlikely to change significantly, but that's not yet guaranteed.

This PR also makes an attempt to support both APIs.

PR Checklist

---

• [x] Includes appropriate unit test(s)
• [ ] Appropriate docstring(s) are added/updated
• [x] Code is (approximately) PEP8 compliant (no longer burned on the dev, thanks to pre-commit!)
• [ ] Issue(s) raised/addressed?

[codecov[bot]]

Codecov Report

Merging #469 (21de34d) into main (9721b23) will decrease coverage by 0.66%. The diff coverage is 48.78%.

@@            Coverage Diff             @@
##             main     #469      +/-   ##
==========================================
- Coverage   70.84%   70.17%   -0.67%     
==========================================
  Files          16       16              
  Lines        1650     1670      +20     
==========================================
+ Hits         1169     1172       +3     
- Misses        481      498      +17     

[mattwthompson]

Hey folks,

The new version of the OpenFF Toolkit has been released, so I'm able to run these tests without pulling in RC/beta builds. I'm not sure why CI isn't running - is it because I'm pushing to a fork?

[mattwthompson]

Tests appear to be fail-fast and failing because we (OpenFF) no longer package on Python 3.7. I opened #513 to possibly mitigate this.

[daico007]

Agree with changing the element arg to symbol, gonna do a quick commit to change the var name

[mattwthompson]

Thanks!